This is not the first time Kofi Annan has found himself charged with maintaining the decorum of polite international diplomacy against a background of mass murder.

Annan was the head of UN peacekeeping operations at the time of its two greatest failures, the genocide of Rwanda Tutsis in 1994 and the killing of up to 8,000 Muslim men and boys from the Bosnian town of Srebrenica in July 1995. In both cases, UN troops under Annan's command were on the ground, and in both cases disastrously failed to save the lives of the civilians they were supposed to protect.

When Annan became UN secretary general in 1997, he commissioned inquiries into the Rwandan and Bosnian debacles which in both cases found the UN secretariat could have done more to prevent the bloodshed. Although Annan offered apologies in both cases, he stayed in his post, as did other UN officials involved.

"A lot of people thought he should have resigned over both Rwanda and Bosnia," said a former diplomat at the UN during Annan's tenure. "In both cases the UN machinery kept the airwaves busy with the appearance of diplomacy while the killings continued and we are in that same situation in Syria."

In January 1994, the commander of UN troops in Rwanda, Canadian Lieutenant General Romeo Dallaire, sent a fax to Annan's department warning of plans for the genocide, including details of weapons caches, three months before the killings began, and stating his intention to carry out raids on the arms stores. He signed off in French: "Where there's a will, there's a way. Let's go."

However, the reply from UN headquarters under Annan's name, instructed Dallaire not to take action and instead inform the Rwandan government of the threat. Dallaire requests to beef up his forces in the effort to protect Rwandan civilians were also denied. Instead, his troop numbers were cut.

Philip Gourevitch, the US author and journalist who first published the UN response to Dallaire, made comparisons with the current situation in Syria in a New Yorker blog on Wednesday.

"In real life, the UN has effectively run cover for the Syrian regime's bloody campaign by deploying Kofi Annan, the weak and accommodating former secretary general, to Damascus," Gourevitch wrote. "The peace plan Annan cooked up with Assad in late March is another soap bubble, and the UN military observers who are supposed to monitor it are useless – or worse: when the butchery began in Houla, the regime told the UN monitors to stay away, which they did, bringing back bad memories, from the mid-nineties, of the false promises of protection that were extended, under the UN flag, to the people of Bosnia and Rwanda before they were abandoned to their killers."

Richard Gowan, an expert on UN peacekeeping at New York University argues that the catastrophic failures in Rwanda and Bosnia were more the responsibility of the major powers on the security council who set the weak mandate of the UN forces in both cases.

"I think it's deeply unfair to define Annan by what happened in Rwanda and Bosnia when you look at many other cases, especially in Africa, in Kenya for example, where he has shown himself to be an effective mediator," Gowan said.

"What is sadly clear in Syria now is that although Russia was willing to green light the Annan mission it is not prepared to follow through, so he is increasingly powerless without Russian support," he said. "But Annan also doesn't want to add Syria to the list of failures. He believes in the need to keep talking under extremely difficult circumstances. He believes the role of the UN is to keep diplomacy going even when all seems lost."

However, other analysts argued that preserving diplomatic niceties in Syria, as in Rwanda and Bosnia before, makes things worse by giving a false impression that the normal mediating mechanisms can ultimately save lives.

"The danger that his peace plan gives a false sense that the international community is really having an impact there, while in fact Assad is carrying out his plan undisturbed. It suggests that there is a diplomatic solution and you just have to be patient," said David Rohde, a commentator for Reuters, who documented the Bosnian slaughter in the book Endgame: The Betrayal and Fall of Srebrenica.

Gowan said Annan now finds himself in a deepening dilemma, with his peace plan stalled and ignored inside Syria, facing a split security council back in New York, and under fire for providing a fig-leaf to mass murder.

"If UN pulls out, on the other hand, and there another escalation of violence, Annan could be accused of walking out on a dialogue too early. So its a lose-lose situation."